House Speaker Kevin McCarthy is a man who stays in motion — enthusiastically greeting tourists at the Capitol, dashing overseas last week to the G7 summit of industrial world leaders, and raising funds back home to elect fellow Republicans to the House majority. But beneath the whirlwind of activity is a stubborn standstill, an imbalance of power between the far-right Republicans who hoisted McCarthy to the speaker’s role yet threaten his own ability to lead the House.